Control logic for fuel controls on APUs

• US 20070095070A1
• Filed: 11/07/2006
• Published: 05/03/2007
• Est. Priority Date: 02/17/2004
• Status: Active Grant

• Current Assignee: Harold Riley
• Original Assignee: Harold Riley
• Inventors: Riley, Harold
• Granted Patent: US 7,340,901 B2
• Time in Patent Office: Days
• US Class Current: 60/773
• CPC Class Codes: F02C 7/26 Starting; Ignition
• CPC Class Codes: F02C 9/28 Regulating systems responsive to plant or ambient parameters, e.g. temperature, pressure, rotor speed F02C9/30 - F02C9/38, F02C9/44 take precedence
• CPC Class Codes: F05D 2220/50 for auxiliary power units (APU's)
• CPC Class Codes: F05D 2270/021 to prevent overspeed
• CPC Class Codes: F05D 2270/095 by temporary overriding set control limits
• CPC Class Codes: F05D 2270/112 by limiting temperatures
• CPC Class Codes: F05D 2270/3032 excessive temperatures, e.g. caused by overheating
• CPC Class Codes: F05D 2270/705 proportional-integral

Abstract

Conventional auxiliary power units (APUs) may experience over-temperature shutdowns when attempting to start them at high altitudes. Further, such conventional APUs may also experience overspeed conditions when a generator load is removed during on-speed operations. A fuel control logic that controls the fuel flow cutback below the minimum blowout fuel schedule is provided. A temperature trim loop measures engine temperature to determine the onset of a possible over-temperature condition. The fuel flow may then be trimmed accordingly to correct this over-temperature onset. Further, when the onset of an overspeed condition is detected, such as when a generator load is removed, the fuel flow may be trimmed accordingly to correct this overspeed onset. The fuel control logic allows the control to find the individual minimum fuel flow for each fuel control without risking blowout of the APU itself.

Claims

1. A method for correcting and/or preventing an overspeed condition in an auxiliary power unit comprising:

measuring the speed of the auxiliary power unit;

comparing the speed to a predetermined speed reference point to determine a speed error;

calculating a fuel flow trim value from the speed error;

subtracting the fuel flow trim value from a commanded fuel flow value to get a trimmed commanded fuel flow value; and

delivering fuel to the auxiliary power unit at said trimmed commanded fuel flow value.

2. The method according to claim 1, wherein the method is used during on-speed operation of the auxiliary power unit.

3. The method according to claim 1, further comprising:

determining a blowout prevention rate;

comparing the trimmed commanded fuel flow value to a predetermined minimum fuel schedule to determine a possibility of blowout at the trimmed commanded fuel flow value; and

providing fuel to the auxiliary power unit at the blowout prevention rate when the possibility of blowout is present, thereby preventing blowout of the auxiliary power unit.

4. The method according to claim 3, further comprising providing an upper limit on the fuel flow trim value at a predetermined maximum fuel schedule.

5. A method for correcting and/or preventing an overspeed condition during on-speed operation of an auxiliary power unit in an aircraft comprising:

measuring the speed of the auxiliary power unit;

comparing the speed to a predetermined speed reference point to determine a speed error;

calculating a fuel flow trim value from the speed error;

subtracting the fuel flow trim value from a commanded fuel flow value to get a trimmed commanded fuel flow value;

providing an upper limit on said the fuel flow trim value at a predetermined maximum fuel schedule;

determining a blowout prevention rate;

comparing the trimmed commanded fuel flow value to a predetermined minimum fuel schedule to determine a possibility of blowout at the trimmed commanded fuel flow value;

delivering fuel to the auxiliary power unit at the blowout prevention rate when the possibility of blowout is present, thereby preventing blowout of the auxiliary power unit; and

delivering fuel to the auxiliary power unit at said trimmed commanded fuel flow value when the possibility of blowout is not present.